The purpose of this study is to assess the safety and efficacy of pembrolizumab (MK-3475) combined with lenvatinib (MK-7902/E7080) compared to pembrolizumab alone (with placebo for lenvatinib) in treatment-naïve adults with no prior systemic therapy for their metastatic non-small cell lung cancer (NSCLC) whose tumors have a programmed cell death-ligand 1 (PD-L1) Tumor Proportion Score (TPS) greater than or equal to 1%. The primary study hypotheses are that: 1) the combination of pembrolizumab and lenvatinib is superior to pembrolizumab alone as assessed by Progression-free Survival (PFS) per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1); and 2) the combination of pembrolizumab and lenvatinib is superior to pembrolizumab alone as assessed by Overall Survival (OS).

As of 30-Jul-2021, active participants, investigator, and sponsor personnel or delegate(s) involved in the treatment administration or clinical evaluation of the participants will be unblinded. Participants will discontinue lenvatinib and placebo, and participants who remain on treatment will receive open-label pembrolizumab only.